I was nervous when our dog (cocker) went in too. She was perfectly fine - she was however tripping her arse off because of a morphine plaster (I don't know if they use those here in the UK though). As soon as the plaster came off, she was fine. She was given painkillers and was fine after a few days.

She was absolutely terrified of the cone of shame, so I never used it - I used baby onesies/bodystockings from H&M (the sleeveless ones) with a hole cut for tail. She loved them.